1. Field of the Invention
The present invention relates to a method for detecting a nucleic acid polymer. More particularly, the present invention relates to a method which permits easy detection of an amount of a nucleic acid polymer in a sample, detection of hybridization, if any, of a probe and a nucleic acid polymer, identification of a base sequence of a nucleic acid polymer, a method for causing two-dimensional orientation of a nucleic acid polymer at the gas-water interface, and further, a novel amphiphilic intercalator used in these methods.
2. Description of Related Art
Diverse and various biological functions observed in cells are effectively expressed by regular orientation of biomolecules. For nucleic acid polymers (DNA, RNA) which code genetic information of an organism, however, the effect of an orientation thereof on expression of biological functions has almost never been studied. One of the reasons is that means to control in vitro the orientation of a nucleic acid polymer has not as yet been established.
As a method for retrieving a target gene sequence in a nucleic acid polymer, or for determining similarities and differences or homology of a plurality of nucleic acid polymers, on the other hand, it is conventionally known that the hybridization method using, as a probe, a single-stranded nucleic acid polymer (DNA or RNA) complementary with a portion of sequence of a target nucleic acid polymer. More specifically, the conventional hybridization method comprises the steps of fixing a single-stranded target nucleic acid polymer onto a nitrocellulose membrane or a nylon membrane, and adding an aqueous solution of a probe nucleic acid polymer labelled with a radioisotope or an enzyme onto the membrane. When the probe nucleic acid polymer is hybridized with the target nucleic acid polymer, only the hybridized probe nucleic acid polymer remains on the membrane after washing. Presence of a searched sequence in the target nucleic acid can be determined by detecting radioactivity from the radioisotope labelled on the probe nucleic acid polymer, or chemiluminescence or color of precipitate produced by the enzyme.
In order to handle a radioisotope, however, it is necessary to acquire a special license, so that this technique is not popularly accepted. Labelling a single-stranded probe nucleic acid polymer with an enzyme requires much costs and labor.
A nucleic acid polymer such as genomic DNA existent in chromosome has a double helix structure comprising complementary base pairs (adenine/thymine and cytosine/guanine for DNA, and adenine/uridine, cytosine/inosine and cytosine/guanine for RNA). For identifying differences in the base sequence between two different nucleic acid polymers, for example, formation of a triple helix has been believed to be effective. However, because of the difficulty to detect formation of a triple helix, this method has not as yet been put to practical use.
Among properties of DNA or RNA as a nucleic acid polymer, there is known an intercalation phenomenon in which a cationic pigment is inserted between neighboring base pairs. However, detection of a nucleic acid polymer (content, hybridization, identification of base sequence, etc.) by the use of this phenomenon has not as yet been conducted.